Method of treating sea water



n d States P flt 2,782,162 7 METHOD OF TREATING SEA WATER No Drawing. Application July 7,1952,

Serial No.297,565 t 12 Claims. (Cl. 210-23 This invention relates to the evaporation of sea water and materials useful therein and is a continuation-inpart of my copending application Serial No. 85,268, filed April 2, 1949 now abandoned. The evaporation of sea water in order to produce fresh water has been practiced for many years, particularly on ocean-going vessels. The sea water is pumped through an evaporating vessel, or a series of such vessels, having a heating coil or coils therein. The requisite heat is supplied by passing steam through the coils.

Sea water contains a very high concentration of cal cium and magnesium salts, which are scale-forming. In some oceans silicon compounds which tend to form silicate scales are also encountered. Upon evaporation of the sea water these salts are, of course, left behind with the result thatthe concentration of solids within the evaporator increases and a large amount of scale is built up on the surface of the steam coil. This reduces the efliciency of theapparatus and requires periodic shutdowns for cleaning.

Various mechanical means for removing the scale have been proposed. Means have been provided forflexing the coil so as to break off the scale and to this end bimetallic structures have been devised, the differential expansion of the two metals being relied upon to flex the coil. So-called shock removal, by cutting off the steam supply and pumping cold water into the evaporator shell so as to chill it, has also been practiced. These methods have had only a limited measure of success. Moreover, they present a problem of sludge removal which is particularly troublesome in double or triple-effect evaporators where the sea water is passed successively through different chambers.

Chemical methods of scale prevention, While wellknown in the treatment of fresh water, have not been successful in sea water evaporators. The treatments f employed for fresh water have such low eflicacy when a plied to sea water evaporators that they may be characte'rized as useless for practical purposes. A little greater suppression of scale-forming may be achieved by increasing the dosage, but even so, the results are still unsatisfactory and the increased cost is alone suflicient to make such treatments prohibitive. What is desired Q is a chemical treatment which will inhibit scale formationand will be sufficiently low in cost to make it commercially feasible.

I have found that sea water may be evaporated and the steam coils kept virtually free from scale by the chemical treatment hereinafter described, at a very low cost. v 1 I employ in my process a water-soluble alkali metal or ammonium molecularly dehydrated phosphate having a ratio of alkali-metal oxide or ammonium oxide to phosphorus pentoxide of from about 0.4:1 to about 2.0:1. This class of materials has been found highly effective for scale prevention in the treatment of fresh water. As above indicated, however, its use in corresponding amounts with sea water is of no substantial value, and

2,782,162 Patented Feb. 19, 1957 pounds is highly efiective and results in what is apparently a synergistic efiect since the effect of the combination is greater than would be expected from the knowledge of the results derived from adding the two materials separately.

I preferably employ still a third constituent, namely a water-soluble derivative of a polyalkylene glycol, in which the polyalkylene glycol molecule contains preferably from 1 to 20 alkylene oxide groups. The polyalkylene glycol derivative may be one of the group consisting of the esters, the ethers, the amines or the amides. Polyethylene glycol moncroleate has been found to be particularly satisfactory. While the, presence of this third constituent is not essential to successful results, its presence is advantageous in two respects: (a) tests indicate that the scale-suppressing or inhibiting power of the phosphate-lignin combination is enhanced and (b) foaming is materially reduced, thereby making it possible to operate at a consistently high water level in the evaporator with corresponding operating advantages yet with- O lillt any objectionable carry-over of salinity into the dist1 ate.

Strangely enough my process and composition offer no observable advantage in the prevention ,of scale deposition from scale-forming fresh waters.

The conditions of use are important. I have found that the temperature of the steam in the coils should not exceed about 250 F. I have also found that the pressure in the vapor space above the sea water in the evaporator should not exceed five pounds per square inch gage and is preferably atmospheric or sub-atmospheric. The treating materials should be introduced at such a point and in such a way as to insure uniform dissemination through the sea water under treatment.

The phosphates although these other salts may be employed.

Preferred phosphates are those within the 'MzozPzOs range of about 0.9:1 to the tripolyphosphate composition having a ratio of 1.7: 1, where M is an alkali metal or the ammonium radical. Those having a ratio from 0.4:1 to 09:1 are usually available as glasses which are acid-reacting in aqueous solution and are decreasingly soluble with the decrease in the amount of alkali metal in the glass and although effective for my purpose, the preparation of a treating solution is renderedsomewhat difficult. Although the pyrophosphates, whichare crystalline materials having a' ratio of alkali metal to P205 of 2:1 are slightly effective in combination with the preferred lignin sulfonic acid derivatives the results do not begin to approach those obtained when the crystalline tripolyphosphates, which have a ratio of 1.7 alkali metal or ammonium oxide to 1 phosphorus pentoxide are used. In my preferred composition I use crystalline sodium tripolyphosphate.

The lignin derivatives The term lignin sulfonic acid derivative as used herein is intended to be inclusive of the various complexes prepared by the drying of paper mill waste sulfite liquor or by treating such liquor so as to form purer lignin compounds as hereinafter more fully described;

The actual structure of lignin and of the lignin sulfonic acid derivativesv is not known. It is known that certain materials are derived as a by-product of the sulfite process, for the. manufacture of paper, apparently from the reaction of the sulfite liquor on the cementingmaterials between the wood fibres. have been called lignins.

The simple drying of waste sulfite liquor therefore produces a. material containing lignin sulfonic acids and salts thereof, together with such materials as Wood sugars, organic: acids and calcium sulfite. I have found These materials that this material is. effective in myv process. but it may;

be desirable touse a purer material. It isknoWn-to, mix the.w.aste-, sulfi'te liquor with lime and then treat it again with, limeto, precipitate the. lignin substances as basic calcium lignin sulfonate compounds. It is also known to treat calcium lignin sulfonates with soda ash so as to; form thesodium salts; Howard patents Re. 18,268, 1,848,292, and 1,856,558. These. latter compounds may be briefly. styled asvv Howard type materials.

It will be understood that limitations of overall costs.

The ratio of components Although the twov constituents, phosphate and lignin, defined above may be employed in a weight ratio of phosphatel compound to lignin compound ranging from about. 0.5:1 to about 4:1 I prefer to use about 1.5 parts by weight of sodium tripolyphosphate and about 1.0 part by weight of lignin sulfonate compound. It is, of course, obvious that theweight ratio of phosphate compound to lignin compound will vary even when the lignin comes from the same source since the lignin compounds are derived from natural sources and the purity and composition may vary from time to time.

7 In my preferred composition, in which I incorporate a water-soluble polyalkylene glycol derivative of the group consisting of esters, ethers, amides and amines, I use' about 115- parts by' weight of sodium tripolyphosphate, about 1;.0"part by weight'of lignin sulfonatecompound, and about- 0.020.l part by weight of a polyethylene glycol mono-oleate. The oleateis deriyedfrom apolyethyleneglycol having a molecular weightof about 200 about 400. I may vary the amount of phosphate from about 1 to 2 parts by weight and the polyethylene glycol mono-oleate from about 0.01 to 0.20"partsby weight, the amount of both these constituents calculatedonthe basis of 1 part lignin sulfonate.

The. polyalkylene glycol derivatives The previously-mentioned derivatives of the polyalk-ylene glycols seem to exert a synergistic effect on the othertwo components of the mixture. Whether they do thisby; producing a better wetting of the copper coils, by-better-dispersion of the lignin, or perhaps by still other mechanisms, I am unable to say, but results, not only astorates of steaming but also as to uniformity of cleanness of test coils, have been improved by the presence of these polyalkylene glycol derivatives.

I have found that the high salt concentrations of sea water limits the polyalkylene glycol derivatives which can be-us'ed and that the polyethylene glycols which are usable as antifoams in fresh water are not necessarily effective as antifoams in sea water and vice versa. For

example, Triton X-100, which consists of octyl phenol' with a polyethylene glycol chain will act as an antifoam at 0.2 to 0.5 p. p. m. in my process but will cause boiler water at 2500 p. p. m. to go over the top of the test column when as little as 0.5 p. p. m. are added. In general, I have found that for salt water evaporators, the longer the hydrocarbon chain (in its class) the more effective is the polyalkylene derivative. Thus octadecyl alcohol is more effective than a commercial solution ofhexadecyl and dodecyl alcohols, while thisin turn is. much; more effective than pure dodecyl alcohol alone. I have also found in general that the, shorter the alkylene oxide chain, the more effective the material appears to be. For example, octadecyl alcoholwith;10; moles of ethylene oxide is an excellent antifoam at 0.1 p. p. m. while with 20 moles of ethylene oxide 0.2 p. p. m. is required andwith 40 moles of ethylene oxide 2; p. p. in, is

necessary.

I a ou t e polye hylene yc l. mono oleates, particularly those i -which the molecular weight of the; polyethylene glycolisabout 200; to about; 400;. are veryeffective in repressing. the foaming of boiling sea water or of- 3% sodium chloride solutions when preentin concentrations of as little as 004 part per million, Polyethylene glycol mono-oleates in which the molecular weight of the polyethylene glycol is. as. great as. 600. have been used but are less effective under'certain conditions, particularly underhigh vacuum. Othersimilar and readily dispersible water-soluble higher esters in which the molecular weight of the polyalkylcne glycol portion varies from about 200 to -600, such as the mono-lauryl ester and the mono-ricinolcic ester are:also good antifoam agents.

I havealso found that the soluble higher ethersof the. polyalkylene glycols' suchas lauryl and oleyl ethers of the polyalkylene glycols in which the polyalkylene glycol portion; of: the ,molecule has a moleculanweight from about 200 to 600 are good antifoams; and are less. likely to. decompose than, the esters. However, they are. re? quired in somewhat higher concentrations than the esters. Underzsomeconditions, such as the presence; of organic dispersives, they seem to lose their effectiveness, hence under such circumstances from 3 to 10 times as. muchv of them. are required as of. the esters. I have discovered that: the. higher. esters and ethers. of other polyalkylene glycols; such asthe. polypropylene glycols as Well as the mixed;polyethylene-polypropylene glycols are roughly equivalent to. their respective polyethylene; glycol derivatives.

The amines. and the. amides of theipolyalkylene: glycols suclras octadecyl. amine with 5 to 10 moles: of. ethylene oxideand' the. oxtadecyl amide with 5 to 10 moles. ofv

ethylene oxide are likewise: suitable polyalkylene' glycol. derivatives: for use in my invention.

, I I have found,,in general, that the preferred material's for use in the composition of; my invention fall within; the followinggroups:

The esters Cm'to C20 .zcid wi'th from 1 to Methylene oxide, groups. C12 to C18.- acidwithifrom 5: to 15 propylene oxldegroups The ethers .C16i to: CmalcohQl with from; 2, to 20 ethylene oxide C'm toCia amines with fronrS to 10 ethylene oxide/groups i The amides Crete C18 amides with from to ethylene oxide groups Conditions of blowdow n i In shipboard use a sea water evaporator will ordinarily be operated at about 67% blowdown; i. e., of every three tons of sea water passed through the evaporator, one ton will be evaporated and two tons will be discharged as waste. Under these conditions the addition of my treating composition in amounts as low as five parts per million has a marked effect and the use of ten parts per million keeps the coils substantially free fromadherent scale.

In some cases it may be deemed desirable to operate with a lesser blowdown, in which case the concentrations should be increased. For a 50% blowdown a concentration of say parts per million will be found desirable and for a 25% blowdown it may be as high as 30 parts per million. It will be understood, however, that the economic margin is very small and that the total cost of the compound employed will be a material factor in determining the operating conditions.

While I have described a present preferred application of my invention, it may be otherwise embodied within the scope of the following claims.

I claim:

1. A method of treating sea water whereby it is rendered less scale-forming when heated which comprises adding thereto an effective amount up to 50 parts per million of a water-soluble molecularly dehydrated phosphate of the group consisting of the alkali metals and ammonium having a molar ratio of group member oxide to phosphorus pentoxide from about 0.4:1 to about 2.011, and a water soluble salt of lignin sulfonic acid.

2. A method of treating sea water whereby it is rendered less scale-forming when heated which comprises adding thereto an effective amount up to 50 parts per million of a water-soluble molecularly dehydrated phosphate of the group consisting of the alkali metals and ammonium having a ratio of group member oxide to phosphorus pentoxide of about 0.421 to about 2.0:1 and a water soluble salt of lignin sulfonic acid, the ratio of phosphate to lignin sulfonic acid salt being about 1:1 to about 2: 1.

3. A method of treating sea water whereby it is rendered less scale-forming when heated which comprises maintaining therein a concentration of about 5 parts per million to about 50 parts per million of a composition comprising a water-soluble molecularly dehydrated phosphate of the group consisting of alkali metals and ammonium having a molar ratio of group member oxide to phosphorus pentoxide of about 0.4:1 to about 2.011 and a water soluble salt of lignin sulfonic acid, the ratio of phosphate I to lignin sulfonic acid salt being between about 1:1 and about 2:1.

4. A method of treating sea water whereby it is rendered less scale-forming when heated which comprises adding thereto an effective amount up to about 50 parts per million of a mixture consisting of a water-soluble crystalline sodium tripolyphosphate and a watersoluble salt of lignin sulfonic acid, the ratio of phosphate to lignin sulfonic acid salt being about 1:1 to about 2:1.

5. A method of treating sea water whereby it is rendered less scale-forming when heated which comprises maintaining therein a concentration of from about 5 fonic acid, the ratio of phosphate to lignin sulfonicacid,

salt being about 0.5 :1 to about 2: l.

6. A method of treating sea water whereby to minimize the scale-forming and foaming characteristics thereof when heated which comprises adding thereto an eifective amount up to about 50 parts per million of a water: soluble molecularly dehydrated phosphate of the group consisting of alkali metals and ammonium, a water soluble salt of lignin sulfonic'acid, and a polyalkylene glycol derivative selected from the group consisting of the'ethers, the esters; the a'n'iin'esand the amides.

. 7. A method of treating sea water whereby to minimize the scale-forming and foaming characteristics thereof when heated which comprises adding thereto an effective amount up to about 50 parts per million of a watersoluble molecularly dehydrated phosphate of the group consisting of alkali metals and ammonium, having a ratio of group member oxide to phosphorus pentoxide of about 0.421 to about 2.0:1, a water soluble salt of lignin sulfonic acid and a polyalkylene glycol derivative in which the polyalkylene glycol molecule has a molecular weight of about 200 to 5000 and selected from the group consisting of ethers, esters, amines and amides.

8. A method of treating sea water whereby to minimize the scale-forming and foaming characteristics thereof when heated which comprises adding thereto an effective amount up to about 50 parts per million of a mixture comprising by weight about 1 to 2 parts water-soluble molecularly dehydrated phosphate of the group consisting of alkali metal and ammonium and having a molar ratio of group member oxide to phosphorus pentoxide of about 0.421 to 2.021, 1 part water soluble lignin sulfonic acid salt and from 0.02-0.20 parts of a polyalkylene glycol derivative in which the polyalkylene glycol molecule contains from 1 to 20 alkylene oxide groups and selected from the group consisting of water-soluble others, esters, amines and amides.

9. A method of treating sea water whereby to minimize the scale-forming and foaming characteristics thereof when heated which comprises adding thereto an effective amount up to about 50 parts per million of a mixture comprising by weight about 1 to 2 parts watersoluble alkali-metal molecularly dehydrated phosphate having a molar ratio of alkali-metal oxide to phosphorus pentoxide of about 0.4:1 to 2.021, 1 part' water soluble lignin sulfonic acid salt and from 0.020.20 parts of a polyalkylene glycol derivative in which the polyalkylene glycol molecule contains from 1 to 20 alkylene oxide groups and selected from the group consisting of watersoluble ethers, esters, amines and amides having from 12 to 20 carbon atoms in the ether, ester, amine and amide group.

10. A method of treating sea water to be used in evaporators to prevent the formation of scale and foaming which comprises adding to the sea water about 5 to 30 parts per million the basis of the feed Water, a composition consisting of about one part of evaporated waste sulfite liquor, 1 to 2 parts of sodium tripolyphosphate and about 002201 parts per million of polyethyylene glycol mono-oleate where the molecular weight of the polyethylene glycol molecule is about 200 to 400.

11. A method of treating sea water to be used in evaporators to prevent the formation of scale and foaming which comprises adding to the sea water about 5 to 30 parts per million on the basis of the feed water, a composition consisting of about 1 part of evaporated waste sufite liquor, 1 to 2 parts of sodium tripolyphosphate and about 002201 parts per million of polyethylene glycol mono-oleate.

12. A method of treating sea water for use in evaporators which comprises adding to the sea water about 5 to 30 parts per million on the basis of the feed water of 7 acomposition consisting of-one. part of evaporated waste su1fite= liquor, 1 to. 2: parts of sodium. tripolyphosphate, and. about0.02:0..1 parts per million of a polyethylene glycol mono-ester where the fatty acid chain contains about 12 to 18 carbon atoms.

References. Cited in the file of this patent UNITED STATES PATENTS 2,248,656 Bird July 8, 1941 2,318,663, Bird May 11, 1943 2,358,222 Fink et a1. Sept. 12, 1944 2,374,100 Jackson Apr. 17, 1945 Gundel son .j Jan. 1, 1946 OTHER REFERENCES Chemicals by Glyco, Pub. of Glyco Pdts. Co., N. Y.,

Polyethylene Glycol Esters, Pub. of Kessler Chem. Co.,

Phila., 1948, pp. 8-9. 

1. A METHOD OF TREATING SEA WATER WHEREBY IT IS RENDERED LASS SCALE-FORMING WHEN HEATED WHICH COMPRISES ADDING THERETO AN EFFECTIVE AMOUNT UP TO 50 PARTS PER MILLION OF A WATER-SOLUBLE MOLECULARLY DEHYDRATED PHOSPHATE OF THE GROUP CONSISTING OF THE ALKALI METALS AND AMMONIUM HAVING AMOLAR RATIO OF GROUP MEMBER OXIDE TO PHOSPHORUS PENTOXIDE FROM ABOUT 0.4:1 TO ABOUT 2.0:1, AND A WATER SOLUBLE SALT OF LIGNIN SULFONIC ACID. 